In a security system, for example, there has been known a method of carrying out an authentication by using the pattern of an individual iris as described in Japanese Patent Publication No. 8-504979 and Japanese Patent Publication No. 2000-23946. The authenticating method using an iris has an advantage that an image can be picked up by a camera in a distant place in no contact with an iris differently from a fingerprint, and has been therefore expected to spread in the future.
An iris image pickup apparatus to be used for an individual authentication employs an automatic focusing technique described in Japanese Patent Publication No. 2000-131598, for example, in order to acquire a clear iris image focused on an iris. The automatic focusing technique utilizes the fact that more high frequency components are included in an image pickup signal when an object is focused so that an outline image is clearly picked up, and searches for a lens position in which the high frequency component included in the picked up image signal has a peak while changing the lens position. In order to rapidly search for a peak position, there is generally employed a so-called mountaineering method for gradually changing the lens position in such a direction that the high frequency component is increased (the search is not carried out in such a direction that the high frequency component is decreased).
A high frequency component included in an image clearly picking up the outline of an iris has a high frequency. For example, therefore, it is possible to find an iris focusing position with high precision by carrying out the search through a high-pass filter H for causing the image pickup signal to pass through 1 MHz to 2 MHz. As shown in FIG. 8, however, a characteristic line VH of a high frequency component passing through the high-pass filter H is almost flat in portions other than a peak point A. In the case in which the peak position is to be searched by employing the mountaineering method, therefore, there is a high possibility that a computer cannot decide whether the search is to be carried out in a rightward direction (the lens position is set in an FAR direction) or a leftward direction (the direction of the lens is set in an NEAR direction), and furthermore, a peak position B caused by a noise might be erroneously detected as a focusing position.
For this reason, if the search is carried out by using, as the high-pass filter, a high-pass filter L for passing through 300 kHz to 2 MHz including a lower frequency band, for example, in place of the high-pass filter H having a narrow band described above, a characteristic line VL is greatly changed vertically as shown in FIG. 8. Consequently, it is possible to easily search for a peak position C by the mountaineering method. Thus, the search can rapidly be carried out. For this reason, in the case in which a focusing position is to be searched by the mountaineering method, the high-pass filter having a great band width is generally used.
In an iris authenticating apparatus to be used for a security system, it is possible to enhance an identification rate corresponding to a clearer iris image which is acquired. On the other hand, an authentication object person to be an object cannot be stationary for a long time. Therefore, it is necessary to focus a lens on the position of an iris in a short time. For this reason, the mountaineering method is usually used for the search in an iris image pickup apparatus to be used for the iris authenticating apparatus.
However, there is a problem if the authentication object person wears glasses. In the case in which the authentication object person wears the glasses, a high frequency component generated from the outline of an iris is hidden because the amount of a high frequency component generated by the frame or illumination reflection of the glasses is larger. Consequently, the image of the iris picked up in the lens position focused on the glasses is blurred or focusing cannot be carried out due to the illumination reflection of the glasses so that the identification rate is reduced.